Vacuum cleaners are provided with a vacuum collection system for creating a partial vacuum to suck up debris (which may include dirt, dust, soil, hair, and other debris) from a surface to be cleaned and for collecting the removed debris in a space provided on the vacuum cleaner for later disposal. Vacuum cleaners are usable on a wide variety of common household surfaces such as soft flooring including carpets and rugs, and hard or bare flooring, including tile, hardwood, laminate, vinyl, and linoleum.
One type of carpet presently gaining in popularity is “super soft” or “ultra-soft” carpet, which is made up of lower denier fibers that are more densely tufted onto a carpet backing than for conventional carpet types such as “plush”, “Berber” or “frieze”, for example. Denier is a measurement of weight; more specifically, denier is the weight in grams of 9,000 meters of a filament, fiber or yarn. Typically, a thinner fiber will weigh less and will have a lower denier than a relatively thicker fiber. The denier of a filament of fibers used in a super soft carpet typically ranges from 3.5 to 5, while the nylon filaments of a conventional carpet have a denier of 12 to 18. The combination of low denier fibers and dense tufting gives a super soft carpet a very soft and plush feel, but can also create difficulties with respect to vacuum cleaning since the densely-packed fibers can impede airflow, which can cause the suction nozzle to suck down and become virtually sealed or “locked down” to the super soft carpet. This nozzle “lock down” condition can increase the push force required to move the vacuum cleaner over the carpet. Additionally, the carpet backing typically used with super soft carpet can be nearly impermeable to airflow, which can exacerbate nozzle lock down and further increase the push force.
Although different carpet types can increase a vacuum cleaner's push force to varying degrees, other aspects, including the structural configuration of the vacuum cleaner, can increase or compound the push force problem. For example, for upright or stick vacuum cleaners the location of the connection between the upright or handle portion and the base portion can transmit a downward component of push force onto the suction nozzle, which can dig the suction nozzle into the cleaning surface thereby increasing the push force. Additionally, rough, worn or scuffed vacuum cleaner housings or the presence of tacky or sticky material on the surface to be cleaned or on the vacuum cleaner housings can further increase push force. Moreover, obstacles on the surface, such as area rugs and thresholds, for example, can also impede free movement of the vacuum cleaner and thus increase push force, at least temporarily, until the obstacle is removed or overcome.